Kinetic Monte Carlo simulation of the nitridation of the GaAs (100) surfaces

We present, in this work, our preliminary results of a systematic theoretical study of the adsorption of N over As-terminated GaAs (100) (2$\times$1) surfaces. We analyzed the changes in the bond-lenghts, bond-angles and the energetics involved before and after deposition. Our results show that the N-atoms will prefer the unoccupied sites of the surface, close to the As dimer. The presence of the N pushes the As dimer out of the surface, leading to the anion exchange between the N and As atoms. Based on our results, we discussed about the kinetics of the N islands formation during epitaxial growth of the III-Nitrides.Comment: 4 pages, 7 figures, accepted for publication in Braz. J. Phys., special number, Proceedings of BWSP-12, 12th Brazilian Workshop on Semiconductor Physic

Ab initio calculation of the dynamical properties of PPP and PPV

In this work, we have calculated the vibrational modes and frequencies of the crystalline PPP (in both the Pbam and Pnnm symmetries) and PPV (in the P21/c symmetry). Our results are in good agreement with the available experimental data. Also, we have calculated the temperature dependence of their specific heats at constant volume, and of their vibrational entropies. Based on our results, at high temperatures, the PPP is more stable in the Pnnm structure than in the Pbam one.Comment: 5 pages, 7 figures, accepted for publication in Braz. J. Phys., special number, Proceedings of BWSP-12, 12th Brazilian Workshop on Semiconductor Physic

Occurrence of Entomophthorales on Spittlebugs Pests of Pasture in Eastern São Paulo State, Brazil

Spittlebugs (Hemiptera: Cercopidae) are the most important pests of pasture in Brazil. Nymphal behavior, i.e. residing in the soil, makes their control with insecticides difficult. Although Entomophthorales fungi occasionally have been found at epizootic levels in spittlebug populations, they have not been cultured, had their incidence levels determined, nor evaluated for pest control potential. The research reported here aimed to evaluate the occurrence of Entomophthorales species on spittlebug pests of pasture in Pindamonhangaba County, São Paulo State, Brazil. Evaluations were carried out in 2 adjacent fields with Brachiaria decumbens and Pennisetum purpureum grasses, respectively, of 5 ha each. Evaluations were done every 4 days from January through February by capturing spittlebug adults on leaves with an entomological sweep net, and the insect samples were kept frozen until examined. Insect abdomens were dissected and observed by microscopy for the presence of hyphae and resting spores. Insects cadavers with sporulating fungus were collected in the field and taken immediately to the lab to isolate the pathogen. Scanning electron microscopy pictures were taken of conidophores, and primary and secondary conidia of both fungi. Furia sp. was found at epizootic levels on Deois schach in the Brachiaria pasture, reaching 80% infected followed by a fall in the insect population. Batkoa sp. was found at enzootic levels (\u3c 10% infected) on Mahanarva fimbriolata in the P. purpureum pasture. Furia sp. also was found to infect another important spittlebug, Deois flavopicta, indicating that it has good potential as a bioinsecticide. Heavy rainfall adversely affected the occurrence of Batkoa sp. in M. fimbriolata populations in P. purpureum pasture

Estimation of molecular weight and polydispersity in conducting polymers using single-molecule force spectroscopy.

Entrada padronizada: HERRMANN JUNIOR, P. S. de P

Doping in poly(o-ethoxyaniline) nanostructured films studied with atomic force spectroscopy (AFS)

The study of intermolecular interactions at interfaces is essential for a number of applications, in addition to the understanding of mechanisms involved in sensing and biosensing with liquid samples. There are, however, only a few methods to probe such interfacial phenomena, one of which is the atomic force spectroscopy (AFS) where the force between an atomic force microscope tip and the sample surface is measured. In this study, we used AFS to estimate adhesion forces for a nanostructured film of poly(o-ethoxyaniline) (POEA) doped with various acids, in measurements performed in air. The adhesion force was lower for POEA doped with inorganic acids, such as HCl and H2SO4, than with organic acids, because the counterions were screened by the ethoxy groups. Significantly, the morphology of POEA both in the film and in solution depends on the doping acid. Using small-angle X-ray scattering (SAXS) we observed that POEA dissolved in a mixture of dimethyl acetamide exhibits a more extended coil-like conformation, with smaller radius of gyration, than for POEA in water, as in the latter POEA solubility is lower. In AFS measurements in a liquid cell, the force curves for a POEA layer displayed an attractive region for pH ≥ 5 due to van der Waals interactions, with no contribution from a double-layer since POEA was dedoped. In contrast, for pH ≤ 3, POEA was doped and the repulsive double-layer force dominated. With AFS one is therefore able to correlate molecular-level interactions with doping and morphology of semiconducting polymers.FAPESPCNPqNanobiotecCT-Hidro (FINEP

Search for squarks and gluinos in events with isolated leptons, jets and missing transverse momentum at s√=8 TeV with the ATLAS detector

The results of a search for supersymmetry in final states containing at least one isolated lepton (electron or muon), jets and large missing transverse momentum with the ATLAS detector at the Large Hadron Collider are reported. The search is based on proton-proton collision data at a centre-of-mass energy s√=8 TeV collected in 2012, corresponding to an integrated luminosity of 20 fb−1. No significant excess above the Standard Model expectation is observed. Limits are set on supersymmetric particle masses for various supersymmetric models. Depending on the model, the search excludes gluino masses up to 1.32 TeV and squark masses up to 840 GeV. Limits are also set on the parameters of a minimal universal extra dimension model, excluding a compactification radius of 1/R c = 950 GeV for a cut-off scale times radius (ΛR c) of approximately 30